Dielectric disc phase-shifter for waveguide



Jan. 22, 1957 ALLEN ET AL 2,779,003

DIELECTRIC DISC PHASE-SHIFTER FOR WAVEGUIDE Filed Sept. 25, 1950 PHASE SHIFTER CD lNVENTORS PHILIP' J. ALLEN N JOHN H. DUNN 9 Wfli ATTORNEYS United States atent DIELECTRIC DISC PHASE-SHIFT ER FOR WAVEGUIDE Philip J. Allen and John H. Dunn, Washington, D. C. Application September 25, 1950, Serial No. 186,622

3 Claims. (Cl. 333-31) (Granted under Title 35, U. S. Code (1952), sec. 266) This invention relates to phase shifting apparatus for use in high frequency transmission systems utilizing hollow waveguides as the transmission means.

More particularly, the present invention relates to phase shifting apparatus for use in hollow Waveguides where the degree of phase shift may be simply and quickly varied.

It is known in the prior art that varying the dielectric constant of the medium in which an electromagnetic wave is travelling will vary the velocity of propagation of the wave travelling therein. This change in velocity causes a change in phase of the Wave.

Hollow wavegiides are utilized as a conduit for electromagnetic energy and placing a piece of low-loss dielectric material within a waveguide will shift the phase of the waves travelling therein for the reasons just described.

The present invention utilizes a low-loss dielectric material to vary the phase shift of the electromagnetic waves within a hollow waveguide in a novel and expeditious way. In one embodiment of the present invention, a plate made of a low-loss dielectric material having nonuniform dimensions is rotatably mounted adjacent a hol-z;

low waveguide and caused to protrude through a slot in the Walls of the waveguide. Revolving the dielectric plate about its axis causes difierent amounts of dielectric material to protrude into the waveguide providing a single and convenient control for varying the phase shift of the" The present invention has its greatest utility when it is desired to continuously vary the apparent phase of the energy within a waveguide at a high rate such as required in directional antenna beam scanning problems where the beam shift is obtained by varying the phase of the energy fed to the antenna elements. By driving the dielectric plate at a high rate of speed, the phase shift of the waveguide energy is quickly varied with ease and simplicity. This was not readily possible with the cumbersome prior art phase shifting devices.

The present invention also makes it possible to simply cause the degree of phase shift to follow a sine wave function. By shaping the dielectric plate in the form of a circular disc and then tapering the cross section of the plate so that the thickness linearly varies from one edge of the plate to the diametrically opposite end, a substantially sinusoidal phase shifting variation is simply obtained.

Accordingly one object of the present invention is to provide anovel and simple phase shifting device for use in hollow waveguide systems.

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Another object of the present invention is to provide a novel and simple phase shifting device for use in hollow waveguide systems for quickly and continuously varying the phase shift of the energy within the waveguide.

Still another object of the present invention is to provide a novel and simple phase shifting device for use in hollow Waveguide systems for causing a continuous sinusoidal variation in phase shift.

A further object of the present invention is to provide a phase shifting device for use in waveguides where no substantial impedance mismatch results.

These and other objects of the present invention will become apparent from the specification and drawings wherein: V

Figure l is a block diagram representing one embodiment of the present invention.

Figure 2 is a front view of one practical embodiment of the present'invention.

Figure 3 is a side view of the embodiment of Figure 2.

Figure 4 is a curve showing the phase shift as the the axis of the dielectric plate or wheel.

Figure 5 is a block diagram representation of another embodiment of the present invention.

Figure 6 is a side view of the variant embodiment illustrated in block form in Figure 5.

Figure 7 is a curve showing the phase shift as the dielectric plates are rotated for two relative positions of the plates.

Figure 8(a) and (b) is a front and side view of an alternative form of dielectric plate.

Figure 9(a) and (b) is a front and side view of another form of the dielectric plate "1.

As represented in Figure 1, the phase shifting device varies the phase of the energy in a waveguide system by an amount As shown in Figures 2-3, the phase shifting device of one embodiment of the present invention comprises a dielectric plate 1 which is mounted on a shaft 4 rotatable about an'axis a-a. The plate 1 is made to project into a hollow waveguide 2 through aslot 3 which runs parallel to the axis A-'-A of the waveguide 2.

Plate 1 is made preferably of a low-loss dielectric material such as polystyrene. The cross-sectional dimension of the plate 1 is made non-uniform as shown in Figure 3 so that as the plate 1 is rotated about axis a-a different amounts of material protrude into the waveguide thereby varying the degree of phase shift caused by the dielectric material inside the waveguide.

The dielectric material is preferably placed in the portion of the waveguide having the greatest electric field intensity since in this position it has the greatest affect on the amount of phase shift produced. For the TE ,o mode in a rectangular waveguide, the portion of maximum electric field intensity ee runs in the center portion of and parallel to the narrow dimension of the waveguide. Accordingly, slot 3 runs parallel to the axis A-A of, and along the center of the wide side of the rectangular waveguide 2. The axis of rotation aa of the plate or wheel 1 is perpendicular to slot 3 so that plate or wheel 1 may readily pass therethrough into the field of greatest electric field intensity of the Waveguide 2.

A slot in the Walls of a waveguide running perpendicular to the magnetic and electric lines of force in a waveguide will not radiate energy into space. Since a loss of energy is obviously undesirable, having a slot so located is clearly preferred. Slot 3 is in such a position for the TE1,0 mode.

The amount of phase displacement caused by inserting a dielectric material into a waveguide depends on the volume of material so inserted, the dielectric constant of the material, and, as previously discussed, on the electric field intensity into which'itis in'serted. For the case Where a circular'dis'c of homogeneous dielectric: material is used whose thickness is varied as shown in Figure 3 of the drawings, the phase displacement is approximately proportional to the mean thickness of the wheel which protrudes'into waveguide l if thewheel is inserted symmetrically into the waveguide and rotatedzaldng an axis which is :perpendicular to the .axisof the waveguide.

The plate or wheel 1 shown in Figures 2-3 will produce a sinusoidal variation 'in-iphase shift as shown in Figured. ,That is to say, .if wheell is rotated at a constant rate, the phase ,shifLwillcontinuously varyaccordjing to a sine function, One revolution of wheel. 1 will produce one-period ofithe sine, function.

As shown in Figure 3, the thickness of wheel 1 is gradually increased'in asymmetricalmanner from one point on the periphery of the Wheel to afpoint on the periphery of the wheeldiametrically opposite thereof. The faces of the plate or wheel 1 are ineffect formed by two in- .jclinedplams; P1, 132 which intersect at a point F which lies along. a line F.Ff which is;perpe ndict 1lar to axis a. afof. wheel 1. Thestructure of wheel is thus simple and economical to construct. 1 p p s lIfitis desired to increasethe amplitude of the sinusoidal phase shift variationgQit is only necessary to increase the d epth to which the wheel l protrudes into waveguide 2.

This is accomplished by nroving the axisabout which plate orw heel 1 rotates closer to waveguide 3 such as oas ins fli- The change in phase shift is shown in Figure 4. With .theaxi s ult qll ia q t n if t e is tated by a constant speed motor fi or byhandpthe phase shift -valiation is shpwnby the lower; curvein Figure 4. The mean phase shift is show n by ordinate c. If the ax s fi m t d. sl w b Waveguide iflisai ai bf the .sinas i a la iat dn is i rsass a n i t mean "phase a since the average volume of dielectric material protruding into waveguide Z i s thereby increased.

The shape of wheel 1 as showh in Figures 2-3 enables one toconveniently change the amplitude of the sinusoidal Phase ift variati n- -Eq som pu Qs ;t.-. dssimsi' qr h n e e y the amplitude of the sinusoidal variation while keeping a conigu idq ljlj andthie lo f ithe I nerg'y is varied according to a sinus'pidal fun on. Thus wheels 1 and 1" are caused to protrude throughfslots 3 and 3' in the iresp ective waveguides. I "two wheels "1.1" are kept fi xedlyi'r'elatedby of ga s iiitable' coupling device 6 which frigidlyconnects'shafts {and 14. p s

If the "wheels 1 1' are in a position corresponding to that shown in Figured, 'so that, the 't wo'wlieels'are in the "same position (relativelto the thi iiess ioi'their cross section) then rotating newnes together will produce identical instantaneous phase'f shifts in waveguides 2,"and 2. The pha'sedifierence (o s-lpzlwould therefore be zero if thejamplitudes of the v sinusoidal pha'se shifts produced in each 'waveguide were equal. I

,..l. h l. .rqt a f' ivq o ,w s ihdpbsition shown by the dotted "l' nesj'in" Fi t es, 'th qagfbeing 'the'difierence of two"like'sinuso1dal waveform displaced in time phase will also be a sinusoidal waveformsh'own by curve 1 in Figure 7.

If the position ofwheel 1' is fixedly positioned relative to wheel 1. to a position between the solid and dotted positions of Figure 6, then the amplitude variation of the relative phase shift 3-2 will be smaller and displaced in phase as shown by curve 2 in Figure 7. The mean phase difierence is still zero. The embodiment of Figures 56 thus provides a simple means for progressively varying the ampitude of the sinusoidal phase shift variation Where the mean phase shift. remains zero,

Although the embodiments of Figures 1-6 disclose a circular dielectric wheel which rotates about an axis at the center thereof whose thickness gradually varies to produce a change in phase shift, other types of wheels may be used, one example of which is shown in Figure 8, if other than a sinusoidal phase shift variationis desired. The wheel 1" there shown comprises a circular disc of constant thickness whose axis of rotation is along a point 7 which is ofi center. The distance the wheel protrudes into'thelwaveguide'is thusvaried'asthe wheel'is rotated.

This design has the disadvantage that one cannot vary the amplitudeover as'wide a limit as in the design where the thickness of thecir'cular wheel is varied as in themeferred emboditiient of Figures l-6.

The largest possible phase shift variation for a single revolution of the dielectric wheel is obtained where the thickness of the wheelof the embodiment of Figure 8 is varied like wheel 1 in'Figure 6. In effect, this is a combinationof the features of the wheel in Figures l-6 with that "of Figure '8.

may be varied. 'Figure9 shows a circular dielectric plate .1" having a constantthickne'ss whose'axis of rotation is in the center thereof. The plate consists of sections '6' -{7 which are made of dielectric materials having different dielectric constants. As plate 1 is rotated, the degree of phase shift varies'b'ecause the ratio of the volume of dielectric material of section 6' to that of section 7 which protrudes into waveguide 2 varies with its angular position.

It is to be noted that the phase shift of energy in waveguide 2 could "also be varied by mounting the, axis of the dielectric wheel parallel to the axis A-A of the waveguide. A slot would then heart in the waveguide running perpendicular to thewaveguide axis A-A. This would be undesirable from many viewpoints. First of all such asl'ot would radiate energy and thereby cause undesirable losses. Secondly, if the wheel would protrude substantially into the 'wave'guide'the problem of mismatch is greatly increased over. that caused by the preferred embodiment of Figures l6.

Although a rectangular waveguide operated in the TE1,0 mode has been disclosechthe present invention has application withother types of waveguides and-modes.

Many other'modifications'may be made of the'specific embodiments first=disclosed without deviating from the soopeof the present invention.

The invention des cribedhere'in may be manufactured and used by m terthe Government of the United States of America for governmental purposes without the payment of any royalties thereon 'or therefor.

What is claimed is: v w

1. Apparatus for producing ha sinusoidal variation in the phase shiftfot energy ina aonsiw waveguidesystem comprising a circular plate made of adielectric material rotatably mounted about a givenaxis, said axis being in the center of said plate, the thickness of said plate gradually increasing in value from one edge to the other diametrically opposite edge; thereof, saidplate protruding into a hollow waveguide through a narrow slot-inthe walls thereof, "said'slot' being-parallel to. the"-axis of the waveguide, "said 'given' aiiis "being perpendicular to said waveguide axis, means for rotating said plate at a constant angular rate whereby the phase of said energy varies continuously according to a sine function.

2. Apparatus for producing a sinusoidal variation in the phase shift of energy in a hollow waveguide system comprising a circular plate made of a low-loss dielectric material rotatably mounted about a given axis, said axis being in the center of said plate, the thickness of said plate linearly increasing in value from one edge to the other diametrically opposite edge thereof, said plate protruding into a hollow waveguide through a narrow slot in the walls thereof, said slot being parallel to the axis of the waveguide, said given axis being perpendicular to said Waveguide axis.

3. Apparatus for producing a sinusoidal variation in the phase shift of energy in a hollow waveguide system comprising a circular plate made of a dielectric material rotatably mounted about a given axis, said axis being in the center of said plate, said plate protruding into a hollow waveguide through a narrow slot in the walls thereof extending lengthwise of said waveguide, the thickness of the portions of said plate which protrude into said slot as said plate is rotated gradually increasing in value from one side of said plate to the diametrically opposite side thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,423,150 Lindenblad July 1, 1947 2,426,992 Folland et al. Sept. 9, 1947 2,433,368 Johnson et a1 Dec. 30, 1947 2,495,170 Kiun Jan. 17, 1950 2,505,557 Lyman Apr. 25, 1950 FOREIGN PATENTS 802,756 France June 13, 1936 591,369 Great Britain Aug. 15, 1947 OTHER REFERENCES Kallmann, H. E.: Standing Wave Meter, Electronics,

20 January 1947, page 96. 

